Is swearing by other than Allah considered major or minor Shirk if there is no intention of Shirk or equating the created with the Creator, and is the one who does so excused for their ignorance of the consequence?

Swearing by Allah is minor shirk, and your assumption does not make it major shirk. The rule is that whoever's Islam is established with certainty, it is not removed except with certainty. We advise you to repent from swearing by other than Allah, and to avert your mind from thinking about this matter, for fear of falling into waswasah (whispers/obsessive thoughts). Major shirk is not limited to believing in a creator other than Allah.